1. Field of the Invention
The present invention relates to a throttle device equipped with a throttle valve for controlling a flow rate of a fluid, in particular, to a throttle device having a cover that is coupled to a throttle body for covering internal elements, such as a reduction gear mechanism.
2. Description of the Related Art
In general, electronically controlled throttle devices include a throttle body and a cover that is mounted to an open end on one lateral side of the throttle body, so that a reduction gear mechanism, a throttle sensor and some other elements of the throttle body are accommodated within the throttle body protected from exposure to the outside. The reduction gear mechanism is adapted to transmit a rotation of an electric motor to a throttle valve in order to incrementally open and close the throttle valve. The throttle sensor is adapted to detect the opening angle of the throttle valve.
Japanese Laid-Open Patent Publication No. 2001-132495 (in particular FIG. 2 of this publication) teaches a conventional structure for mounting a cover to a throttle body. In this mounting structure, the cover is placed so as to abut an annular mount portion defining a lateral open end of the throttle body and is then fastened to the throttle body by means of a plurality of screws at multiple positions along a circumferential direction.
Japanese Laid-Open Patent Publication No. 2001-303979 (in particular FIG. 2 of this publication) teaches a different conventional mounting structure, in which a cover is coupled to a throttle body by using a resilient engaging mechanism or a snap-fit mechanism that includes a plural set of projections and a recesses that engage with each other.
However, the former conventional mounting structure using screws to secure the cover requires a number of separate parts. Therefore, the overall manufacturing costs are increased. In addition, it takes much time for the assembly process of inserting and correctly tightening the screws. Therefore, the mounting operation cannot be performed relatively efficiently.
In case of the latter conventional mounting structure using resilient members or typical snap-fit connections, the projection can be easily disengaged from their recesses by a manual operation or by using a simple tool. Therefore, if a cover has been intentionally or accidentally removed from a throttle body of a throttle device by a user, after being assembled and tested by the manufacturer, a possibility exists that when the cover is reinstalled by the user, misalignment or damage to the throttle sensor and other internal components may cause malfunctioning of the engine, or a reduction of life of the throttle body device.